Borehole Fracture Research Articles

Spatial and Temporal Distribution Law and Influencing Factors of the Mining‐Induced Deformation and Failure of Gas Boreholes

Because gas boreholes are easy to damage by integrated coal mining and gas exploration, based on the practice of relieving pressure in deep thin coal seams in the Huainan mining area, a multidimensional coupling numerical simulation method was used to reveal the space‐time evolution characteristics and influence factors of fracture deformation of gob‐side gas boreholes. Results indicate that the danger zone for borehole fractures is primarily between 5 and 12 m above the roof of the roadway. The final‐hole position has little effect on the stability of boreholes, and migrating the open‐hole position to the entity coal side and roadway roof side can improve the stability of the borehole. The initial failure of the borehole occurs at a distance of 10 m behind the coal face. The failure of the borehole is largely stable at a distance of 100 to 120 m behind the coal face. With the increase in mining height, which leads to an increase in the movement of strata and an increase in pressure relief range, the shear stability of the borehole is reduced, and the extrusion stability of the borehole is improved. A hard roof condition promotes borehole shear stability, while a weak roof condition promotes borehole extrusion stability. This change can decrease the maintenance difficulty associated with “minor supports” in boreholes to a certain extent by reinforcing the support strength of “primary supports” in roadway retaining walls. The simulation results are consistent with observed results for the 11 test boreholes, and the accuracy of the numerical simulation is verified.

Characterization of Hydraulic Fractures Growth During the Äspö Hard Rock Laboratory Experiment (Sweden)

A crucial issue to characterize hydraulic fractures is the robust, accurate and automated detection and location of acoustic emissions (AE) associated with the fracture nucleation and growth process. Waveform stacking and coherence analysis techniques are here adapted using massive datasets with very high sampling (1 MHz) from a hydraulic fracturing experiment that took place 410 m below surface in the Aspo Hard Rock Laboratory (Sweden). We present the results obtained during the conventional, continuous water injection experiment Hydraulic Fracture 2. The resulting catalogue is composed of more than 4000 AEs. Frequency–magnitude distribution from AE magnitudes (MAE) reveals a high b value of 2.4. The magnitude of completeness is also estimated approximately MAE 1.1, and we observe an interval range of MAE between 0.77 and 2.79. The hydraulic fractures growth is then characterized by mapping the spatiotemporal evolution of AE hypocentres. The AE activity is spatially clustered in a prolate ellipsoid, resembling the main activated fracture volume (~105 m3), where the lengths of the principal axes (a = 10 m; b = 5 m; c = 4 m) define its size and its orientation can be estimated for a rupture plane (strike ~123°, dip ~60°). An asymmetric rupture process regarding to the fracturing borehole is clearly exhibited. AE events migrate upwards covering the depth interval between 404 and 414 m. After completing each injection and reinjection phase, the AE activity decreases and appears located in the same area of the initial fracture phase, suggesting a crack-closing effect.

Mechanism of rock burst induced by fault slip in an island coal panel and hazard assessment using seismic tomography: a case study from Xuzhuang colliery, Xuzhou, China

Rock burst hazards induced by fault slip frequently occur in underground mining and threaten the safety of miners. In this paper, the structures of overlying strata, mechanism of fault slip, and rock burst pre-warning using seismic tomography were investigated in LW7192, a specific island longwall panel in Xuzhuang Colliery. The results show that an asymmetrical “T” structure of overlying strata is formed during LW7192 retreat, and the long hanging length of overlying key strata is maintained due to the short panel width. By analysing a modified fault sliding model, it is found that the time interval between two fault slips has a positive correlation with the energy released therein. The rock burst that occurred in LW7192 has the longest time interval between events compared with other high-energy tremors near the fault, and enormous elastic energies released by fault slip as a form of dynamic load. The superposition of dynamic loads and high stress concentration of the coal-rock mass contributes to the rock burst in LW7192. For forecasting rock burst hazards, seismic tomography was used and the results show that the velocity anomaly regions correspond well with the area of both strong tremors and the rock burst. Ultimately, large-diameter boreholes, directional hydraulic fracturing boreholes, and floor distressing boreholes were taken in the rock burst area, and the pressure relief is proved effective by seismic tomography assessment.

Comprehensive analysis of initiation and propagation pressures in drilling induced fractures

A new experimental set-up was designed to carry out high-pressure borehole fracturing tests on cylindrical rock samples. The experimental set-up offers full control over borehole, confining, and pore pressures. Fracturing experiments were conducted on cylindrical Berea sandstone samples. Several injection cycles were carried out on each rock sample to measure the Fracture Initiation Pressure (FIP) and the stable Fracture Propagation Pressure (FPP) at various confining pressures. The measured FIP values were compared with Hubbert and Willis’ model, and Rummel's model. The stable FPPs were measured using synthetic based mud (SBM) with and without lost circulation material (LCM), and compared with the large-scale fracturing experiments conducted at the Drilling Engineering Association (DEA) 13 investigation. Our study shows that initiation of a drilling induced fracture (DIF) is best characterized by a fracture mechanics approach such as Rummel's model. The stable FPP value changes linearly with the minimum horizontal stress (Shmin), and it is independent of the maximum horizontal stress (Shmax) or the vertical stress (Sv). Also, we show that adding LCM to the drilling fluids significantly enhances the stable FPP.

Optimum particle size distribution design for lost circulation control and wellbore strengthening

In this paper, we have experimentally studied the impact of particle size distribution (PSD) on the fracture sealing capability of lost circulation material (LCM) blends. Our primary aim was to determine the PSD which maximizes the Wellbore Strengthening (WBS) benefits obtained from fracture sealing. High-pressure borehole fracturing experiments were conducted on Berea sandstone samples under atmospheric pore pressure and various confining pressures to investigate the WBS effects of several LCM blends. Post-fracturing methods such as Computerized Axial Tomography (CAT) scan and thin-section imaging were used to investigate the geometry of induced fractures and formed seals within them. Based on the conducted experiments and post-fracturing analyses, we have evaluated and re-assessed well-known theories applicable to the design of LCM blends, such as the one-third rule, the ideal packing theory, and the Vickers criteria. Our experiments indicate that for any rock with a given set of rock strength and failure parameters, there exists an optimum PSD to maximize WBS benefits. Optimum PSD appears to be of primary importance, almost independent of LCM type. In addition, we have shown that the optimum PSD should have a bimodal structure, with sufficient concentrations of properly sized fine and coarse particles. Although the one-third rule, the ideal packing theory, and the Vickers criteria may provide some basic PSD guidelines, these theories are mainly empirical relationships based on conventional particle plugging experiments. As shown here, they do not properly represent the physics of fracture sealing. To remedy this situation, we are introducing a new family of design curves for optimum PSD, based on the underlying physics of fracture sealing observed in the WBS experiments.

Experimental Study of Crack Initiation and Extension Induced by Hydraulic Fracturing in a Tree-Type Borehole Array

High-pressure hydraulic fracturing technology in coal and coal bed methane mines can lead to roof and floor damage, and fracture initiation disorder that leads to a “blank area”, and other issues. A new method of hydraulic fracturing is proposed to increase the homogeneous permeability of coal in underground coalmines. Numerical and other simulation tests for different forms of a tree-type, branched borehole model are presented. The results show that the branched array causes cracks to initiate from the bottom of the array, and these extend along the direction of the adjacent boreholes. Generally, as the number of branched boreholes increases, the coal seam fracture network also increase, improving the distribution of the fracture network, making the fracturing effect better. The branched boreholes appear to reduce initiation pressure and, with increasing branches, the initiation pressure decreases. A model with four tree-type, branched boreholes leads to a reduction in initiation pressure of 69%. In terms of permeability improvement technology in underground coalmines, a branched hydraulic fracturing borehole array has the advantages of reducing initiation pressure, controlling crack initiation and extension, enhancing the fracturing effect and reducing the destruction of the roof and floor.

Fracture size estimation using data from multiple boreholes

The size of a fracture within a rock mass can be obtained using data sampled from boreholes or exposed surfaces. In this study, fracture sizes are estimated using data from multiple boreholes. The fractures are assumed to be elliptical, all having the same aspect ratio, but not necessarily occurring parallel to each other. Formulae for estimating the mean and standard deviation of the characteristic fracture size are developed by considering the number of intersections between the fractures and the boreholes. A method is proposed to infer the probability density function of the fracture size from the number of fractures, which is obtained by random sampling of fractures in adjacent boreholes; the fracture distribution is assumed to follow the form of a fractal, exponential, or lognormal distribution. The performance of the method is validated using Monte Carlo simulations with different inputs of size distribution, fracture density, orientation, and mean fracture size.

Study on effect of in-situ stress ratio and discontinuities orientation on borehole stability in heavily fractured rocks using discrete element method

Abstract Borehole instabilities pose significant challenges in drilling and completion operations, specifically in the areas where pre-existing fractures are intersected by the borehole. In-situ stresses play a vital role in failure mechanism around an excavation. In addition, discontinuities increase the probability of instability. Therefore analyses of effect of in-situ stress in discontinuous media have significant importance in identifying efficient drilling methodologies. Numerical investigation on the behaviour of an unsupported vertical cylindrical borehole in heavily fractured rock mass is presented in this study. Discrete Element Model (DEM) based code Universal Distinct Element Code (UDEC) is used as the simulation tool. With taking into account the in-situ stress conditions in Cooper basin, South Australia, an unsupported borehole of 0.15 m radius in the centre of the model was simulated comprising of two fracture sets. The vertical stress applied correlates with the 1.5 km depth of the Cooper basin. The effect of fracture orientation and in-situ horizontal stress ratio (σH/σh) on the stability of the rock mass around the borehole was investigated. It has been shown that the induced stresses due to excavation lead to the development of a yielded zone around the borehole. Borehole stability criteria relevant to the extent of yielded zone and maximum displacement around the borehole were introduced into stability analysis. Results show that when the in-situ stress ratio increases the rock blocks at borehole wall tend to move towards the centre of borehole, consequently yielded zone around the borehole increases. Similarly, the fracture orientation changes the angle of borehole fracture intersection which aids in displacement increase as well as the location of block detachment. Furthermore the change in fracture orientation highly influences the formation of yielded zone.

Fracture identification based on remote detection acoustic reflection logging

Fracture identification is important for the evaluation of carbonate reservoirs. However, conventional logging equipment has small depth of investigation and cannot detect rock fractures more than three meters away from the borehole. Remote acoustic logging uses phase-controlled array-transmitting and long sound probes that increase the depth of investigation. The interpretation of logging data with respect to fractures is typically guided by practical experience rather than theory and is often ambiguous. We use remote acoustic reflection logging data and high-order finite-difference approximations in the forward modeling and prestack reverse-time migration to image fractures. First, we perform forward modeling of the fracture responses as a function of the fracture–borehole wall distance, aperture, and dip angle. Second, we extract the energy intensity within the imaging area to determine whether the fracture can be identified as the formation velocity is varied. Finally, we evaluate the effect of the fracture–borehole distance, fracture aperture, and dip angle on fracture identification.

Characterisation of the transmissivity field of a fractured and karstic aquifer, Southern France

Geological and hydrological data collected at the Terrieu experimental site north of Montpellier, in a confined carbonate aquifer indicates that both fracture clusters and a major bedding plane form the main flow paths of this highly heterogeneous karst aquifer. However, characterising the geometry and spatial location of the main flow channels and estimating their flow properties remain difficult. These challenges can be addressed by solving an inverse problem using the available hydraulic head data recorded during a set of interference pumping tests.We first constructed a 2D equivalent porous medium model to represent the test site domain and then employed regular zoning parameterisation, on which the inverse modelling was performed. Because we aim to resolve the fine-scale characteristics of the transmissivity field, the problem undertaken is essentially a large-scale inverse model, i.e. the dimension of the unknown parameters is high. In order to deal with the high computational demands in such a large-scale inverse problem, a gradient-based, non-linear algorithm (SNOPT) was used to estimate the transmissivity field on the experimental site scale through the inversion of steady-state, hydraulic head measurements recorded at 22 boreholes during 8 sequential cross-hole pumping tests. We used the data from outcrops, borehole fracture measurements and interpretations of inter-well connectivities from interference test responses as initial models to trigger the inversion. Constraints for hydraulic conductivities, based on analytical interpretations of pumping tests, were also added to the inversion models. In addition, the efficiency of the adopted inverse algorithm enables us to increase dramatically the number of unknown parameters to investigate the influence of elementary discretisation on the reconstruction of the transmissivity fields in both synthetic and field studies.By following the above approach, transmissivity fields that produce similar hydrodynamic behaviours to the real head measurements were obtained. The inverted transmissivity fields show complex, spatial heterogeneities with highly conductive channels embedded in a low transmissivity matrix region. The spatial trend of the main flow channels is in a good agreement with that of the main fracture sets mapped on outcrops in the vicinity of the Terrieu site suggesting that the hydraulic anisotropy is consistent with the structural anisotropy. These results from the inverse modelling enable the main flow paths to be located and their hydrodynamic properties to be estimated.

Flexible gel (FG) for gas-drainage drilling sealing material based on orthogonal design

Aiming to resolve the technical problems of lower gas concentrations and a reduced effective drainage period caused by gas-drainage borehole fracture development, a flexible gel (FG) gas-drainage borehole sealing material was developed that adapts to borehole deformation. In this study, based on orthogonal tests, the effect of the ratio of material to water, stirring time and stirring speed on the viscosity, filtration property, water retention and pumpability of the FG were studied. The results indicate that the stirring speed, ratio of material to water and stirring time in turn increased the viscosity and the ratio of material to water, stirring time and stirring speed enhanced the filtration property and water retention. The FG pumps smoothly and achieves the optimal state of high water retention, low fluid loss and low viscosity when the ratio of material to water is 1:10, the stirring speed is 800r/min, and the stirring time is 12min. The field test results indicate that, after using the FG, the average drainage gas concentration increases by 25.9% and 27.6% and the average negative pressure of extraction increases by 2.7kPa and 3.5kPa compared with expansive cement and polyurethane, respectively.

Closed form flow model of a damped slug test in a fractured bedrock borehole

Summary An existing closed form model is modified to describe the damped response of groundwater in a fractured bedrock borehole with variable apertures and dips to a slug test. The existing theory, which requires single sized horizontal fractures, is accurately calibrated by slug test data from three uncased bedrock boreholes in the Dedham Granite and an observation well screened just below the contact surface with a till drumlin. Apertures and dips vary however, so the ability of the modified theory to accommodate different sizes and inclinations improves upon the physical validity of its predecessor when fracture information accompanies slug test data. Geophysical logs identify a large number and dip of fractures in the uncased boreholes in the Dedham Granite in this regard. A lognormally distributed, horizontal aperture calibration of the slug tests in the uncased boreholes retains the accuracy of the single size model, and yields aperture statistics more consistent with literature values. The slug test in the screened observation well is accurately calibrated with the modified horizontal theory for discrete (two) sizes, based upon the average fracture spacing found in the uncased boreholes. All four results yield comparable compressibility estimates, which depend on fracture spacing but not size or dip. The calibrated aperture size and calculated fracture porosity and permeability decrease with length of the borehole into the Dedham Granite. The measured dip and aperture for flowing and nonflowing fractures in one of the boreholes accurately calibrates the modified theory. The inclusion of dip reduces the calibrated permeability because of the increased ellipsoidal area at the interface of the borehole and the inclined fractures.

A novel method of orienting hydraulic fractures in coal mines and its mechanism of intensified conduction

With increasing coal mining depth, coal-bed methane (CBM) extraction becomes increasingly difficult, especially for underground CBM extraction. This paper proposes a method for the efficient extraction of CBM in underground coal mines that orients a borehole around a hydraulic fracturing borehole, uses a high-pressure water jet to perforate parallel to the coal bed inclination in the boreholes, and finally performs hydraulic fracturing. Because of shear failure at the perforation tip, cracks initiate at the perforation tip during hydraulic fracturing. Moreover, the perforation causes the maximum principal stress at an angle approximately parallel to the perforation axial, which leads to the orderly propagation of the crack in the coal. The initiation pressure of hydraulic fracturing with and without perforation is compared. Under the same stress combination, the initiation pressure is lower for boreholes with perforation than for boreholes without perforation. The initiation pressure also depends on both the ratio between the maximum horizontal principal stress and the vertical stress and the ratio between the maximum and minimum horizontal principal stresses. Additionally, perforation can effectively stress the coal seam, which extends the crack closure time. Field experiment results show that after hydraulic fracturing with the novel method, the gas drainage volume increased by a factor of 11.26, and the drainage concentration increased by a factor of 2.12 compared with the ordinary gas drainage method.

Discrete 3D fracture network extraction and characterization from 3D seismic data — A case study at Teapot Dome

Three-dimensional discrete fracture networks (DFNs) extracted from the seismic data of the Tensleep Formation at Teapot Dome successfully matched 1D fracture data from multiple boreholes within the area. The extraction process used four seismic attributes, i.e., variance, chaos, curvature, and spectral edge, and their multiple realizations to define seismic discontinuities that could potentially represent fractures within the Tensleep Formation. All of the potential fracture attributes were further enhanced using a fracture-tracking attribute for better extraction and analysis of seismic discontinuity surfaces and their network properties. A state-of-the-art discontinuity surface extraction and characterization workflow uniformly extracted and interactively characterized the seismic discontinuity surfaces and networks that correlate with borehole fracture data. Among the attributes, a fracture-tracking attribute cube created out of the high-resolution spectral-edge attribute provided the best match with the borehole fracture data from the Tensleep Formation. Therefore, the extracted discontinuity planes were classified as fractures and then characterized. The extracted fracture population also matched earlier published records of faults and fractures at Teapot Dome. Unlike the conventional method, which uses 1D borehole fracture data as primary input and 3D seismic data as a guide volume during DFN modeling, I used 3D seismic attributes as the primary data and the 1D borehole fracture data only for quality control. I also evaluated the power of converting seismic fracture attribute volumes into discrete surfaces and networks for effective correlation with 1D fracture logs from boreholes.

Analysis on the Initial Cracking Parameters of Cross-Measure Hydraulic Fracture in Underground Coal Mines

Initial cracking pressure and locations are important parameters in conducting cross-measure hydraulic fracturing to enhance coal seam permeability in underground coalmines, which are significantly influenced by in-situ stress and occurrence of coal seam. In this study, stress state around cross-measure fracturing boreholes was analyzed using in-situ stress coordinate transformation, then a mathematical model was developed to evaluate initial cracking parameters of borehole assuming the maximum tensile stress criterion. Subsequently, the influences of in-situ stress and occurrence of coal seams on initial cracking pressure and locations in underground coalmines were analyzed using the proposed model. Finally, the proposed model was verified with field test data. The results suggest that the initial cracking pressure increases with the depth cover and coal seam dip angle. However, it decreases with the increase in azimuth of major principle stress. The results also indicate that the initial cracking locations concentrated in the second and fourth quadrant in polar coordinate, and shifted direction to the strike of coal seam as coal seam dip angle and azimuth of maximum principle stress increase. Field investigation revealed consistent rule with the developed model that the initial cracking pressure increases with the coal seam dip angle. Therefore, the proposed mathematical model provides theoretical insight to analyze the initial cracking parameters during cross-measure hydraulic fracturing for underground coalmines.

3D geostatistical modeling of fracture system in a granitic massif to characterize hydraulic properties and fracture distribution

This study integrates 3D models of rock fractures from different sources and hydraulic properties aimed at identifying relationships between fractures and permeability. The Tono area in central Japan, chiefly overlain by Cretaceous granite, was examined because of the availability of a unique dataset from deep borehole data at 26 sites. A geostatistical method (GEOFRAC) that can incorporate orientations of sampled data was applied to 50,900 borehole fractures for spatial modeling of fractures over a 12km by 8km area, to a depth of 1.5km. GEOFRAC produced a plausible 3D fracture model, in that the orientations of simulated fractures correspond to those of the sample data and the continuous fractures appeared near a known fault. Small-scale fracture distributions with dominant orientations were also characterized around the two shafts using fracture data from the shaft walls. By integrating the 3D model of hydraulic conductivity using sequential Gaussian simulation with the GEOFRAC fractures from the borehole data, the fracture sizes and directions that strongly affect permeable features were identified. Four fracture-related elements: lineaments from a shaded 10-m DEM, GEOFRAC fractures using the borehole and shaft data, and microcracks from SEM images, were used for correlating fracture attributes at different scales. The consistency of the semivariogram models of distribution densities was identified. Using an experimental relationship between hydraulic conductivity and fracture length, the fractures that typically affect the hydraulic properties at the drift scale were surmised to be in the range 100–200m. These results are useful for a comprehensive understanding of rock fracture systems and their hydraulic characteristics at multiple scales in a target area.

Strength criterion for rocks under compressive-tensile stresses and its application

Estimating in-situ stress with hydraulic borehole fracturing involves tensile strength of rock. Several strength criteria with three parameters result in tensile strengths with great differences, although they may describe the relation between strength of rock and confining pressure with low misfits. The exponential criterion provides acceptable magnitudes of tensile strengths for granites and over-estimates that for other rocks, but the criterion with tension cut-off is applicable to all rocks. The breakdown pressure will be lower than the shut-in pressure during hydraulic borehole fracturing, when the maximum horizontal principal stress is 2 times larger than the minor one; and it is not the peak value in the first cycle, but the point where the slope of pressure-time curve begins to decline.

The mechanics and physics of fracturing: application to thermal aspects of crack propagation and to fracking.

By way of introduction, the general invariant integral (GI) based on the energy conservation law is presented, with mention of cosmic, gravitational, mass, elastic, thermal and electromagnetic energy of matter application to demonstrate the approach, including Coulomb's Law generalized for moving electric charges, Newton's Law generalized for coupled gravitational/cosmic field, the new Archimedes' Law accounting for gravitational and surface energy, and others. Then using this approach the temperature track behind a moving crack is found, and the coupling of elastic and thermal energies is set up in fracturing. For porous materials saturated with a fluid or gas, the notion of binary continuum is used to introduce the corresponding GIs. As applied to the horizontal drilling and fracturing of boreholes, the field of pressure and flow rate as well as the fluid output from both a horizontal borehole and a fracture are derived in the fluid extraction regime. The theory of fracking in shale gas reservoirs is suggested for three basic regimes of the drill mud permeation, with calculating the shape and volume of the local region of the multiply fractured rock in terms of the pressures of rock, drill mud and shale gas.

A novel ECBM extraction technology based on the integration of hydraulic slotting and hydraulic fracturing

Because most coal mines in China have high gas content with low permeability, it is necessary to increase the efficiency of the CBM extracting technology. Enhanced coalbed methane (ECBM) recovery is a suitable option in this regard. This paper demonstrates a novel ECBM extraction technology, which involves the integration of hydraulic slotting (HS) and hydraulic fracturing (HF). The efficiency of the method is evaluated by field test. The slots produced by the HS method are used to control the extension direction of fracture cracks, and the efficiency of CBM extraction from the single drilling is improved by performing slotting drilling in coordination with fracturing drilling. The numerical software Coupled Analysis of Flow and Solid Mechanics in Rock Failure Process Analysis (RFPA2D-Flow) was used to analyse the direction of the crack propagation in the HF process. The coal-crack-propagation process, hydraulic gradient evolution, acoustic emission phenomena, and the change in the stress of coal body with the propagation of the fracturing crack were studied. The results of the study show that because the water pressure around the fracture bore is affected by the slots created, the hydraulic gradient in the horizontal direction is larger than that in the vertical direction, and the cracks more easily extend along the direction of the larger hydraulic gradient following the initiation of the cracks. After HF, a fully unloading area, a transition pressure-relief area, and the original stress area around the fracturing boreholes are formed. Results of the field test show that once the ECBM extraction is completed, the coal-seam disturbance range of the single drilling increases, and the CBM extraction efficiency is significantly improved. This novel ECBM extraction technology is a very promising method for improving the effect of the CBM extraction in the field.

Optimization and application of sealing material and sealing length for hydraulic fracturing borehole in underground coal mines

Considering the problems happening to sealing materials for hydraulic fracturing borehole in underground coalmines, such as shrinkage, poor sealing effect, high cost, and improper sealing length, a new hydraulic fracturing sealing material consisting of cement, early strength water-reduced agent, polypropylene fiber, and mixing water is under development. Through indoor laboratory experiment, the sealing material ratio at the optimum compressive strength and shrinking percentage is optimized. A mechanical model for hydraulic fracturing borehole sealing has also been established, which leads us to the relationship between the maximum water pressure that can be carried by sealing materials and such sealing parameters as properties of materials and sealing length. A proper sealing length is determined and verified through a site experiment. The result demonstrates that the optimal ratio of the new material is 1:0.6:0.03:0.005 for concrete, water, early strength water-reduced agent, and polypropylene fiber, respectively. The maximum water pressure that can be carried by the sealing material amplifies with the increase of the strength, elasticity modulus of the sealing material, and sealing length until a constant value is nearly attained when the sealing length reaches a certain point. In addition, taking Chongqing Songzao mining area in China for example, the reasonable sealing lengths of the fracture borehole for through beds fracturing and along beds fracturing are proved to be 10 and 13 m, respectively, which is consistent with theoretical analysis.